Fiber-size emulsion and use thereof



United States Patent FIBER-SIZE EMULSION AND USE THEREOF Robert C. Olson, Cloquet, Minn., assignor to Wood Conversion Company, St. Paul, Minn., a corporation of Delaware No Drawing. Application January 9, 1951, Serial No. 205,233

7' 8,Claims. (Cl. 92-2l) paperboards and wallboards, it has long been a practice to mix a dispersion of wax, or rosin, or both into a furnish of fibers to be felted. In some cases a stable dispersion is employed to which is then added alum or some other precipitant to exhaust or break the dispersion and release the disperse phase for application of the size as solid material to the fibers. On heating the fibers with the deposited size, as is usually done in drying wet felts, the size melts and permeates the fiber to impart water-resistance or-other desired properties.

Improvements in the art have resulted in the provision of less stable dispersions which are substantive to the fibers so that on mixing dispersion into the fiber furnish the dispersion is exhausted and the disperse phase discharged and deposited on the fibers without need to add a precipitant. This is action resulting from surface phenomena well understood by technicians skilled in the art. Such practice is described in the U. S. patent to Neitzke No. 2,096,129. Neitzke provides dispersions, which employ the opposing forces of a dispersion stabilizer and of a precipitant which in the absence of the stabilizer will effect precipitation of the dispersed phase. Electrical charges are involved and they are such that certain surfaces overcome the stabilizing effect of the stabilizer and assist the precipitating effect of the precipitant. Such dispersions are said to be substantive to those surfaces which induce precipitation. As stabilizer, Neitzke employs water-soluble agents such as gum arabic or a neutral salt of 'sulphonic acid which is inert toward and non-precipitable by such electrolytes as aluminum sulphate, aluminum chloride, sodium aluminate, ferric chloride and ferric sulphate, which are examples of Neitzkes electrolyte precipitant which deposits the sizing material on surfaces in action likened by him to mordanting a dyestuff.

The Neitzke patent describes dispersions which already incorporate an electrolyte salt which is a precipitant and which have a dispersion stabilizer. These substantive dispersions are compounded to render the dispersion per se stable, yet unstable in contact with sensitive surfaces in which the electric charge disrupts and breaks the dis persion. Many materials have surfaces which are sensitive to deposition thereon of the disperse phase of such a dispersion, for example, metal as in the walls of a metal container, minerals, wood, and vegetable fibers. Such a substantive dispersion may be prepared in a large quantity and stored in a metal or other container for future use. The container walls may induce deposition thereon initially, but when once fully coated the induction ceases. Thus, there may be made and stored a large supply to be drawn upon for adding dispersion in given proportion to fiber in a suspension in water for a felting operation. This is highly advantageous in that the operations of proportioning, adding and distributing 2,754,206 Patented July 10, 1956 a precipitant into a mixture of fiber and dispersion are eliminated.

The present invention involves a substantive dispersion of the kind stated employing bentonite as the dispersion stabilizer to prevent the electrolyte exerting its normal action to discharge or precipitate the dispersed sizing material, until the presence of a surface to which it is substantive overcomes the stabilizing force. In certain uses of such a dispersion difficulties are sometimes encountered and other times not encountered. The problem thus presented arose without knowledge of its cause and study of it has led to a solution hereinafter described. The problem appeared as follows:

In the process of forming high grade coated decorative wallboard from wood fibers, as described in Heritage U. S. Patent No. 2,409,628, and using a size deposited from a substantive dispersion stabilized with bentonite, many areas of a coated board were found to be defective. The defective areas are necessarily culled from the production line, thereby involving extra labor for culling and higher cost for usable production. The defect consisted of small areas varying from Vs inch to $6 inch in diameter in the form one would describe as grease spots" with or without a dark speck in the center. Such a coated board was made by adding a bentonite stabilized wax-rosin dispersion, containing alum, to the fiber furnish, felting the furnish on a Fourdrinier type of machine, compressing the wet felt to a wet structuralboard-forming mat, coating onto the wet mat an aqueous suspension of mineral pigment in a protein dispersion, and drying the wet and wet-coated mat in an oven. In the oven the described defects appeared.

lnvestigation established that some grades of bentonite produced this defect and others did not. The grades are differentiated by particle-size analysis. The finer grades produced a limited amount of visible defect requiring a small percentage of cull, and certain coarser grades enormously increase the cull in production. The studies have established that mineral particle impurities suspended in a substantive dispersion induce precipitation thereon of a coat of the dispersed material. In felting fibers coated by action of such a dispersion, some of the coated mineral particles are caught at the surface of the felt by the filtering action of the felt. This filtering is enhanced in proportion as the dispersed material contains wax, because the lower specific gravity of the wax tends more to fioat the particle and minimize the chances that it will finally rest within the mat and not on its surface. When these size-coated particles at ornear the surface are heated in drying the felted product, the particle nucleus loses its coat by melting and the spreading of the melted size renders the location visible at the surface. When the particle is at the surface, the mineral nucleus itself may be visible as a speck according to its physical size. This action of melting of size and spreading with resulting visibility occurs in any felted sheet, coated or not. The visibility is enhanced to the degree that the refractive index of the pigment differs from the refractive index of the size. In coated sheets, such as decorative wall board where the coating material is applied as a fluid before the coated nucleus has been heated, the latter may or may not float or be moved to the face of the coating material. If so, then on heating the freed nucleus is exposed as a speck centered in a size-spot. Otherwise there are size-spots of varying size, according to the depth at which the nucleus lies, or according to the size of the nucleus which predetermines the amount of size-material locally concentrated by it, or according to the thickness of the coating and its permeability to the melted size.

Accordingly, it is an object of the present invention to 3 provide bentonite-stabilized dispersions with bentonite selected so as to avoid appearance of resulting defects.

It is a particular object of the invention to provide substantive dispersions for fibers which are stabilized with bentonite characterized by nuclei of mineral impurities limited in particle size.

It is also an object of the invention to form an ovendry fiber felt from an aqueous suspension of fiber, sized from a substantive emulsion stabilized with bentonite carrying nuclei of mineral impurities limited in particle size.

Various other and ancillary objects and advantages of the invention will become apparent from the following description and explanation of the invention as it is more particularly described with reference to the commercial manufacture of waliboard.

The active ingredient of bentonite from which its characteristic qualities derive is a clay mineral known as montmorillonite. Bentonite is the family name of clays which have montmorillonite as their chief constituent. The remaining mineral content is commonly known as grit and may be any. one or more of feldspar, gypsum, calcium carbonate, quartz, altered volcanic glass, biotite, mica, magnetite, limonite, hematite, leucoxene, apatite, zircon, pyrite, titanite and tremolite. Commercially, the bentonites have approximately from 5% to of such mineral impurities.

Commercial bentonite is commonly sold by its sievesize, the finer the grades the more costly the material. In a process of the kind described for making wallboard, the finest grades produce no visible defects with a corresponding higher cost, while the coarser grades at lower 7 cost produce less useful products on account of the cull involved.

There are several ways of designating the sieve-size of bentonite. One is by a dry screen analysis, and the other is by a wet screen analysis. In screen analysis, the material is sifted through a series of screens varying relatively from coarse to fine. The analysis is expressed in terms of the screens or the size opening thereof, and the percentage of the material remaining on the screens and passing through the screens. In the following Table I there are shown four specimens of bentonite A, B, C and D analyzed by the wet screen procedure, employing three screens respectively of 100, 200 and 325 mesh, of which the size of openings are respectively 150, 74 and 44 microns. In Table I, the first three horizontal lines show the percentage of the material retained on the three screens, and the bottom line shows the percentage of the material passing through all three screens.

TABLE I Percent on piled screens Mesh oi Screen Micron Size ABCD board. The process of said Heritage Patent No. 2,409,628

has been employed. Using the grades A, B and C, less than 1% of cull in production has been found, but in using grade D the cull is approximately 5%, with spots ranging from A; inch to 9% inch in diameter. By reference to the analysis, such suitable grades A, B and C are therefore identified as having by wet-screen analysis at least 96.2% of it finer than 44 microns in size and 'not over 0.3% of it more than microns in size.

Formula No. 1

Parts by weight The rosin and the wax are melted together at a suitable temperature, such as 290 F. The bentonite is mixed with hot water, for example at E, which is run into the melted size with stirring. This mixture is then passed through a colloid mill which fixes and stabilizes the emulsion. The colloid mill discharges emulsion into a storage tank after which the alum of the formula is added. This substantive emulsion may be stored without loss of stability for at least 48 hours when its temperature is controlled, for example at 140 F. On cooling to a temperature solidifying the originally emulsified material, the dispersion ceases to be an emulsion because the dispersed phase is no longer liquid.

For use in making wallboard, a measured quantity of the stored dispersion is mixed into a known quantity of fiber in a furnish to be felted, and automatically the dispersion is exhausted and the disperse phase deposited on the fibers. and variation in it only varies the degree of waterproofness or other property which is desired. A practical range of usage is from .5 to 3 parts of size solids per 100 parts of fiber.

It is to be understood that the size solids may vary from 100% wax to 100% rosin, or any mixture of these. The use of bentonite as emulsion stabilizer permits this variation over limitations which are otherwise imposed when using water-soluble emulsion stabilizers. The content of size solids in the stored dispersion may be as high as 66% and as low as a trace, but approximately 24% is the preferred concentration for facility in compounding in certain available equipment. The precipitant may be any one of the electrolytes known for the purpose, such asaluminum sulfate, aluminum chloride, sodium aluminate, ferric chloride and ferric sulfate.

Although the invention has been described by particular reference to mineral-coated wallboard, it is to be ob served that such material is a desirable interior decorative product wherein the described defects must be lacking. In the absence of processing to coat the said board, as by drging it in an oven directly from its felting operation, the same defects occur. The objectionable material is present in the same way as when a coating is used.

It is also to be understood that the defect described is a phenomenon arising from size-coated grit particles which are located on or very near the surface of the felt, whereas those which are located well into the interior of a thick felt have no effect on visibility. Since the structural-wallboard is about 16 inch thick, only a small proportion of the coated nuclei present may be efiective in causing the defect. .Yet when the finished fiber felt is thinner than wallboard, as when thin sheets of paper or paperboard are made, all of the sized grit particles are effective, not only at one face, but at both faces of the sheet. Since each large nucleus concentrates on it an appreciable quantity of size solids, it is obvious that the appearance of spots is lessened as the sizes of the nuclei diminish.

Accordingly, the invention is not limited to the particular use of the dispersion wherein the defect has arisen and its problem solved. It is to be understood that the invention applies generally to the field of felted fiber products wherein sizing dispersions are employed, and in the appended claims such practices are contemplated.

I claim: ,1. A stable oil-in-water type of emulsion substantive The quantity of size applied is not critical,

to cellulosic fibers consisting essentially of water, a dispersed phase which is sizing material selected from the group consisting of hydrocarbon wax and rosin, said selected material being present in amount up to 66% by weight of the emulsion, dissolved electrolyte salt normally tending to function as a precipitant of the dispersed material which salt is a precipitant selected from the group consisting of aluminum sulphate, aluminum chloride, sodium aluminate, ferric chloride and ferric sulphate, and as dispersion stabilizer a form of the mineral bentonite providing active montmorillonite and grit, the said bentonite being selected from forms thereof having by wet screen analysis at least 96,2% by weight of its particles finer than 44 microns, and not over .3% of its particles larger than 150 microns.

2. The method which comprises forming an oil-in-water type of emulsion which is substantive to fiber and which has up to 66% by weight of a dispersed phase of sizing material selected from the group consisting of hydrocarbon wax and rosin, and which contains dissolved electrolyte salt normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as emulsion stabilizer in quantity to prevent the normal functioning of the electrolyte precipitant, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns and not over .3% of its particles larger than 150 microns, cooling said emulsion to provide a stable dispersion normally substantive to the surfaces of fibers and to the surfaces of the grit content of the bentonite, whereby sizing material is deposited on the surface of the grit particles forming grit-centered bodies of sizing material suspended in the otherwise stable dispersion, mixing said dispersion into a furnish containing fibers to which the dispersion is substantive whereby to effect deposition of sizing material on the fibers, felting the sized fibers to a wet felt suitable for drying whereby the grit-centered bodies are incorporated in the felt, and drying the resulting wet felt at a temperature sufiiciently high to melt the sizing material, whereby the resulting dried faces of the felt are substantially free from visible defective areas resulting from local concentration of sizing material deriving from sized particles of grit substance natural to the bentonite.

3. The method which comprises forming an oilinwater type of emulsion which is substantive to fiber and which has up to 66% by weight of a dispersed phase of sizing material selected from the group consisting of hydrocarbon wax and rosin, and which contains dissolved electrolyte salt normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as emulsion stabilizer in quantity to prevent the normal functioning of the electrolyte precipitant, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns and not over .3% of its particles larger than 150 microns, cooling, said emulsion to provide a stable dispersion normally substantive to the surfaces of fibers and to the surfaces of the grit content of the bentonite, whereby sizing material is deposited on the surface of the grit particles forming gritcentercd bodies of sizing material suspended in the otherwise stable dispersion, mixing said dispersion into a furnish containing fibers to which the dispersion is substantive whereby to effect deposition of sizing material on the fibers, felting the sized fibers to a wet felt suitable for drying whereby the grit-centered bodies are incorporated in the felt, coating said wet felt with an aqueous coating composition permeable when dry to the melted sizing material, and drying the resulting wet and wet-coated felt at a temperature sufiiciently high to melt the sizing material, whereby the resulting coated face is substantially free from visible defective areas resulting from local concentration of sizing material deriving from sized particles of grit substance natural to the bentonite.

4. The method which comprises forming an oil-inwater type of emulsion which is substantive to fiber and which has up to 66% by weight of a dispersed phase of sizing material selected from the group consisting of hydrocarbon wax and rosin, and which contains dissolved electrolyte salt normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grid-containing bentonite as emulsion stabilizer in quantity to prevent the normal functioning of the electrolyte precipitant, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns and not over .3% of its particles larger than microns, cooling said emulsion to provide a stable dispersion normally substantive to the surfaces of fibers and to the surfaces of the grit content of the bentonite, whereby sizing material is deposited on the surface of the grit particles forming grit-centered bodies of sizing material suspended in the otherwise stable dispersion, mixing said dispersion into a furnish containing fibers to which the dispersion is substantive whereby to effect deposition of sizing material on the fibers, felting the sized fibers to a wet felt suitable for drying whereby the grit-centered bodies are incorporated in the felt, coating said wet felt with an aqueous coating composition of suspended pigment and of dispetsed binder material to bind the pigment particles together and to the fibers on drying, and drying the resulting wet and wet-coated felt at a temperature sufliciently high to melt the sizing material, whereby the resulting coated face is substantially free from visible defective areas resulting from local concentration of sizing material deriving from sized particles of grit substance natural to the bentonite.

5. A stable oil-in-water type of aqueous dispersion substantive to fiber and having as the dispersed phase up to 66% by weight of sizing material selected from the group consisting of hydrocarbon wax and rosin, said dispersion comprising dissolved electrolyte salt normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as dispersion-stabiilizer, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns and not over .3% of its particles larger than 150 microns.

6. A stable oil-in-water type of aqueous dispersion substantive to fiber and having as the dispersed phase up to 66% by weight of sizing material selected from the group consisting of hydrocarbon wax and rosin, said dispersion comprising aluminum sulphate normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as dispersion-stabilizer, the hentonite having by wet screen analysis at least 96.2% of its particles finer than 44microns and not over .3% of its particles larger than 150 microns.

7. A stable oil-in-water type of aqueous dispersion substantive to fiber and having as the dispersed phase up to 66% by weight of sizing material consisting of a major portion of hydrocarbon wax and a minor portion of rosin, said dispersion comprising dissolved electrolyte salt normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as dispersion-stabilizer, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns and not over .3% of its particles larger than 150 microns.

8. A stable oil-in-water type of aqueous dispersion substantive to fiber and having as the dispersed phase up to 66% by weight of sizing material consisting of a major portion of hydrocarbon wax and a minor por tion of rosin, said dispersion comprising aluminum sulphate normally tending to function as a precipitant to break the dispersion and discharge the material of the dispersed phase, and grit-containing bentonite as dispersion-stabilizer, the bentonite having by wet screen analysis at least 96.2% of its particles finer than 44 microns 2,417,924 and not over 3% of its particles larger than 150 microns. 2,433,193

. 2,460,787 References Cited in the file of this patent UNITED STATES PATENTS 188 241 1,821,856 Spafi'orcl Sept. 1, 1931 8821562 1,894,959 Manson Ian. 24, 1933 2,096,129 Neitzke Oct. 19, 1937 2,099,880 Ellis Nov. 23, 1937 1 2,158,987 Maloney May 16, 1939 2,242,289 De Laney May 20, 1941 York (1937). 2,266,637 Hauser Dec. 16, 1941 2,343,065 Kumler Feb. 29, 1944 2,409,628 Heritage Oct. 22, 1946 15 New York.

' 8 Gary Mar. 25, 1947 Bechtner Dec. 23, 1947 Seedorf Feb. 1, 1949 FOREIGN PATENTS Great Britain Feb. 23, 1933 France June 8, 1943 OTHER REFERENCES Manufacture of Pulp and Paper, 3rd ed., vol. IV.

Sec. 5, pages 12 and 13, published by McGraw-Hill, New

Manufacture of Pulp and Paper, 3rd ed., vol. IV., Sec.

5, pp. 2, 15-17 (1937), published by McGraw-Hill, 

1. A STABLE OIL-IN-WATER TYPE OF EMULSION SUBSTANTIVE TO CELLULOSIC FIBERS CONSISTING ESSENTIALLY WATER, A DISPERSED PHASE WHICH IS SIZING MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON WAX AND ROSIN, SAID SELECTED MATERIAL BEING PRESENT IN AMOUNT UP TO 66% BY WEIGHT OF THE EMULSION, DISSOLVED ELECTROLYTE SALT NORMALLY TENDING TO FUNCTION AS A PRECIPITANT OF THE DISPERSED MATERIAL WHICH SALT IS A PRECIPITANT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM SULPHATE, ALUMINUM CHLORIDE, SODIUM ALUMINATE, FERRIC CHLORIDE AND FERRIC SULPHATE, AND AS DISPERSION STABILIZER A FORM OF THE MINERAL BENTONITE PROVIDING ACTIVE MONTMORILLONITE AND GRIT, THE SAID BENTONITE BEING SELECTED FROM FORMS THEREOF HAVING BY WET SCREEN ANALYSIS AT LEAT 96,2% BY WEIGHT OF ITS PARTICLES FINER THAN 44 MICRONS, AND NOT OVER .3% OF ITS PARTICLES LARGER THAN 150 MICRONS. 